FIG. 4 is a configurational diagram showing an example of the prior-art controller of a generator for a vehicle, which has the function of variably controlling a regulated voltage and which is stated in, for example, Japanese Patent No. 3,102,981.
The controller shown in FIG. 4 illustrates one example of the controller of the generator for the vehicle, which variably controls the regulated voltage to a voltage corresponding to a duty ratio, on the basis of a control signal that continuously and variably controls the regulated voltage at the duty ratio of 0-100% and that has been inputted through a single signal line from an external control unit.
Referring to FIG. 4, numeral 1 designates an AC generator which is driven by an engine not shown, and which is configured of armature coils 101 and a field coil 102. Numeral 2 designates a rectifier which performs the full-wave rectification of the AC output of the AC generator 1 so as to output a rectified voltage from a + side terminal 201 and a − side terminal 202, and numeral 3 a voltage regulator which controls the rectified AC generator output to a predetermined value.
Numeral 4 designates an external control unit, which controls the ON/OFF operation of a transistor Q1 by a control signal (hereinbelow, also termed the “duty signal”) that can regulate a duty ratio to be outputted from a transistor 401, to 0%-100%.
One end of an operating resistor 318 is connected to the cathode of a Zener diode ZD3 whose anode is grounded, while the other end of the operating resistor 318 is connected to the plus side terminal of a storage battery 5 through a key switch 8. Numeral 321 designates a charging resistor which is connected to the collector of the transistor Q1, numeral 322 the discharging resistor of a capacitor Ce, and numeral 327 the base resistor of the transistor Q1.
The voltage regulator 3 further includes the following configuration:
More specifically, it includes voltage division resistors 319 and 320 which are connected in series between the voltage detection terminal of the storage battery 5 and the ground; a voltage division resistor 317 which is connected in series with voltage division resistors 310-312 that set reference voltages for comparators CP1 and CP2; a comparator CP3 for controlling an ordinary regulated voltage, which compares a point-F voltage (a voltage divided by the voltage division resistors 319 and 320) that changes depending upon a generated voltage and the reference voltage of a point E as is determined by the values of the voltage division resistors 310-312 and 317, and which outputs an L level signal to a transistor Q3 through a diode D5 and turns OFF the transistor Q3 when (the point-F voltage>the point-E voltage) has held; and a comparator CP4 for controlling a regulated voltage based on an external signal, which compares the point-F voltage and a point-A voltage that is set while being updated by the duty ratio of the duty signal, and which outputs the L level signal to the transistor Q3 through a diode D6 and turns OFF the transistor Q3 when the point-F voltage has become greater than the point-A voltage on that occasion.
Besides, it includes a transistor Q4 which is fed with an H level signal through its base resistor 326 and performs an ON operation when the outputs of the comparators CP1 and CP2 are both at an H level, thereby to ground the output of the comparator CP3 connected to its collector, through its emitter; a diode D4 which has its cathode connected to the output terminals of the comparators CP1 and CP2 and has its anode connected to the output terminal of the comparator CP4, and which turns ON and invalidates the output of the comparator CP4 when the output of the comparator CP1 or CP2 is at an L level; and supply voltage pull-up resistors 323-325 which pull up the levels of the output terminals of the respective comparators CP1-CP4 in a plus direction.
Next, the operation of the prior-art apparatus configured as stated above will be described.
First, a constant-voltage supply voltage obtained by closing the key switch 8 and operating the Zener diode ZD3 is applied to individual supply voltage terminals e. As a result, divided voltages generated at a point C, the point E and a point B through which the voltage division resistors 310, 311, 317 and 312 are connected in series are inputted to the respective comparators CP1-CP3 as reference voltages.
Here, the operations of the comparators CP1 and CP2 will be described.
The point-A voltage and the reference voltages of the points C and B are compared by the respective comparators CP1 and CP2.
More specifically, when (the point-A voltage<the point-B voltage) holds, the output of the comparator CP2 becomes the L level, and the output of the comparator CP1 becomes the H level. Further, when (the point-B voltage<the point-A voltage<the point-C voltage) holds, both the outputs of the comparators CP1 and CP2 become the H level, and when (the point-C voltage<the point-A voltage) holds, the output of the comparator CP1 becomes the L level, and the output of the comparator CP2 becomes the H level.
In addition, when at least either of the outputs of the comparators CP1 and CP2 is the L level, the output of the comparator CP4 whose reference voltage is the point-A voltage correlative to the signal level from the external control unit is invalidated, and the output of the ordinary voltage controlling comparator CP3 whose reference voltage is the divided voltage based on the voltage division resistors 310-312 and 317 is validated.
Besides, when both the outputs of the comparators CP1 and CP2 are the H level, the output of the comparator CP3 is invalidated, and the output of the comparator CP4 is validated.
On account of the above operating states, in a case where the duty ratio of the duty signal which is the control signal inputted from the external control unit 4 to the voltage regulator 3 is set into a range from 0% to a duty ratio at which a voltage level is raised to the point-B voltage level being a first predetermined value, at the point A, (the point-A voltage<the point-B voltage) holds while the duty ratio is within the set range, and the output of the comparator CP2 becomes the L level, whereas the output of the comparator CP1 becomes the H level.
Besides, in a case where the duty ratio of the control signal is set into a range from a duty ratio at which the voltage level at the point A is brought to the point-C voltage level being a second predetermined value, to 100%, (the point-C voltage<the point-A voltage) holds while the duty ratio is within the set range, and the output of the comparator CP2 becomes the H level, whereas the output of the comparator CP1 becomes the L level.
As a result, the output of the comparator CP4 becomes invalid, and the output of the comparator CP3 is inputted to the transistor Q3 through the diode D5.
In addition, while the generated voltage does not arrive at an ordinary regulated voltage of 14.4 V and (the point-E voltage>the point-F voltage) holds, the transistor Q3 turns ON and causes a field current to flow through the field coil 102, thereby to continue a power generation operation and to charge the storage battery 5.
When the generated voltage arrives at 14.4 V, the output of the comparator CP3 becomes the L level and turns OFF the transistor Q3, thereby to lower the field current and to weaken the power generation output.
Further, when (the point-B voltage<the point-A voltage<the point-C voltage) holds, both the outputs of the comparators CP1 and CP2 become the H level and turn ON the transistor Q4, thereby to invalidate the output of the comparator CP3 and to input the output of the comparator CP4 to the transistor Q3 through the diode D6.
Accordingly, when the duty ratio of the control signal is changed so as to change the voltage level of the point A within a range of from, at least, the point-B voltage level to the point-C voltage level, the point-A voltage at a level corresponding to the duty ratio is inputted to the + input terminal of the comparator CP4, and the point-F voltage proportional to the generated voltage is inputted to the − input terminal thereof.
In addition, when the voltage level of the point-F voltage proportional to the generated voltage arrives at the point-A voltage level corresponding to the duty ratio, the comparator CP4 inputs the L level signal to the transistor Q3, thereby to turn OFF the transistor Q3.
Besides, when the duty ratio is changed to alter the level of the point-A voltage, the comparator CP4 outputs the L level signal to the transistor Q3 on condition that the point-F voltage arrives at the point-A voltage level corresponding to the altered duty ratio.
As stated above, according to the prior-art apparatus in FIG. 4, the regulated voltage of the generator can be set at any desired value by regulating the duty ratio of the duty signal which is the control signal inputted from the external control unit 4 to the voltage regulator 3.    Patent Document 1: U.S. Pat. No. 3,102,981 (FIGS. 2 and 3)